Nanocellulose surface coated support material

ABSTRACT

The present invention relates to a process for the production of a surface coated support material wherein said process comprises contacting a support material with an aqueous dispersion of nanocellulose. The surface coated support material can be used in a composite material. The invention therefore further relates to the surface coated support material per se, a composite comprising the material, a process for the production of the composite material and an article produced from the composite material.

The present invention relates to a process for the production of ananocellulose surface coated support material

Research interest in utilising natural fibres, such as plant fibres asreinforcement for polymers is re-emerging in the field of engineering.Natural fibres have a number of advantages including their worldwideavailability, high specific strength and modulus, low density,biodegradability and renewability. A particular application of suchreinforced polymers is their use in composite materials.

A composite is a structural product made of two or more distinctcomponents. While each of the components remains physically distinct,composite materials exhibit a synergistic combination of the propertiesof each component, resulting in a material with extremely favourable anduseful characteristics. Composites are generally composed of a matrixcomponent and a reinforcement component. The reinforcement provides thespecial mechanical and/or physical properties of the material and isprovided as fibres or fragments of material. The matrix surrounds andbinds the fibres or fragments together to provide a material which isdurable, stable to heat, stable to corrosion, malleable, strong, stiffand light. Composites made with synthetic fillers such as glass orcarbon fibres are extensively used for many applications, such as sport,automotive and aerospace. Their success is due to their specificproperties, based on a strong interaction between the differentcomponents and a great stability.

The strength and stiffness of a composite material will depend on thestrength and stiffness of the reinforcement component and itsinteraction with the matrix component. A weak mechanical interactionbetween the reinforcement component and the matrix component results ina composite material with limited practical applications. Improving theinteraction of the reinforcement and the matrix components thereforeprovides composite materials which are stronger, more durable and lesssusceptible to stress and wear.

There are however a number of problems associated with the use ofnatural fibres to reinforce polymers, including the inherent variabilityin dimensions and mechanical properties of the fibres, even within thesame cultivation. In addition, the use of natural fibres in compositeshas been limited by their low thermal stability, the resulting reductionin tensile properties after processing and their inherent hydrophilicnature. Attempts to render natural fibres more hydrophobic (therebyimproving the compatibility between hydrophilic natural fibres andhydrophobic polymer matrices) have included silylation (Mehta G, DrzalLT, Mohanty AK, Misra M. J Appl Polym Sci. 2006;99(3):1055-1068; GananP, Garbizu S, Llano-Ponte R, Mondragon I. Polym Compos.2005;26(2):121-127; Pothan L A, Thomas S, Groeninckx G. Compos Pt A-ApplSci Manuf. 2006;37(9):1260-1269; and Valadez-Gonzalez A, Cervantes-Uc JM, Olayo R, Herrera-Franco P J. Compos Pt B-Eng. 1999;30(3):321-331),acetylation (Tserki V, Zafeiropoulos N E, Simon F, Panayiotou C. ComposPt A-Appl Sci Manuf. 2005;36(8):1110-1118), benzoylation (Nair K C M,Thomas S, Groeninckx G. Compos Sci Technol. 2001;61(16):2519-2529),maleated coupling agents (Mishra S, Naik J B, Patil YP. Compos SciTechnol. 2000;60(9):1729-1735), isocyanate treatment (George J,Janardhan R, Anand J S, Bhagawan S S, Thomas S. Polymer.1996;37(24):5421-5431) and polymer grafting of natural fibres (Kaith BS, Kalia S. Express Polym Lett. 2008;2(2):93-100). While these methodshave improved the hydrophobicity of the natural fibres, these chemicaltreatments involve the use of large amounts of hazardous chemicals andthe chemical waste must be handled and disposed of appropriately. Thisadds extra cost to the production of (modified) natural fibre reinforcedcomposites.

Cellulose or plant fibres have been used in some applications in the artas reinforcement agents, such as the manufacture of paper. There are anumber of sources of cellulose fibres. Cellulose microfibrils can beextracted from wood pulp or cotton. Cellulose whiskers called tunicincan also be extracted from tunicate, a sea animal. Finally, bacterialcellulose or nanocellulose can be produced by specific bacteria strains,the most efficient producer being Acetobacter xylinum.

The present invention provides a novel process for the production of amaterial reinforced with nanocellulose.

The first aspect of the invention therefore provides a process for theproduction of a surface coated support material; comprising

-   -   contacting a support material with an aqueous dispersion of        nanocellulose.

It will be appreciated that the nanocellulose for the purposes of thisinvention is isolated nanocellulose (i.e. where the nanocellulose isbacterial cellulose, the support material is contacted with an aqueousdispersion of bacterial cellulose in the absence of a celluloseproducing microorganism). The nanocellulose is therefore extracted,isolated and/or purified prior to the formation of the aqueousnanocellulose dispersion.

For the purposes of this invention, nanocellulose is crystallinecellulose with at least one dimension (i.e. height, length or depth)smaller than 100 nm. The source of the nanocellulose is not limited. Thenanocellulose can therefore be extracted from a plant, such as wood pulpor cotton or can be extracted from an animal such as tunicate.Alternatively, cellulose can be produced by bacteria. The nanocellulosecan be provided as nanofibrillated cellulose, cellulose nanowhiskers orbacterial cellulose.

The nanocellulose can be purified prior to its contact with the supportmaterial. Where the nanocellulose is bacterial cellulose, the bacteriacellulose can be purified by treatment with basic conditions to removeall microorganisms. Alternatively, the cellulose can be purified bycentrifugation.

The nanocellulose can be extracted from a source thereof for example afood stuff such as Nata-de-coco or can be isolated from a bacterialculture of a cellulose producing microorganism. Examples of such acellulose producing micro-organism include micro-organisms belonging tothe genera, Acetobacter, Rhizobium, Alcaligenes, Agrobacterium, Sarcinaand/or Pseudomonas. The micro-organism can be a strain adapted toculture in agitated conditions, such as Acetobacter xylinum BPR2001.

The shape and size of the cellulose will depend on the source of thecellulose. The cellulose is preferably provided as a nanofibre having athickness of from 0.5 to 50 nm, preferably from 1 to 20 nm, morepreferably from 2 to 10 nm, most preferably 1, 2, 3, 4, 5, 6, 7, 8, 9 or10 nm. The cellulose fibre preferably has a width of from 0.5 to 100nm,preferably 1 to 50 nm, more preferably 5 to 20nm. The cellulose fibrepreferably has a length of 0.5 micrometres to 1000 micrometres,preferably 1 micrometres to 500 micrometres, more preferably 5 to 300micrometres, most preferably 10 to 150 micrometres. The cellulose ispreferably produced as a nanofibre, such as a ribbon shaped nanofibril

The nanocellulose is provided in the form of an aqueous dispersion,suspension or a slurry. Thus, the majority of the nanocellulose will notdissolve in the aqueous solution. The dispersion can be prepared bymixing the nanocellulose with an aqueous solution, for example water.The nanocellulose can be mixed with the water by agitation, for exampleby stirring, sonication, colloid milling, grinding or homogenisation.

The support is contacted with the aqueous dispersion of nanocellulose,preferably the support is immersed or dipped in the aqueous dispersionof nanocellulose (i.e. by slurry dipping). The support is preferablybrought into contact with the aqueous dispersion of nanocellulose atroom temperature for a period of from 1 to 2 hours, to 7 days, forexample from 1 to 7 days, such as 2 to 5 days, preferably 3 days. Itwill be appreciated by a person skilled in the art that the timerequired to allow coating of the support will depend on thehydrophilicity and/or water uptake of the support. As a general guide,the minimum amount of time required will be the time required to obtainmaximum moisture saturation of the support when immersed in water.

The support is provided as a polymer. In particular, the support can beprovided as a pellet, a powder, loose fibres, a woven or non-woven fibremat, a string or a tow. The polymer is preferably a reinforcementcomponent or matrix component as used in the art for the manufacture ofcomposite materials. For the purposes of this invention, the support ispreferably a hydrophilic support.

The support is preferably provided in the form of a fibre, pellet or apowder, more preferably as a fibre. The polymer can be a syntheticpolymer or a naturally derived or occurring polymer. In particular, thepolymer may be a naturally occurring fibre or a synthetic polymer basedfibre. For the purposes of this invention, the polymer is preferably ahydrophilic polymer (i.e. the polymer provides hydrogen-bonding sites).

The polymer can be a synthetic bioderived polymer such as poly(lacticacid) (PLA), polyhydroxyalkanoate (PHA), bacterial polyesters orsynthetic, semi-synthetic or modified cellulose polymers such ascellulose acetate butyrate (CAB), cellulose butyrate, polypropylene(PP), polystyrene (PS), polymethylmetharylate (PMMA), Lyocell or rayon.The polymer can be a naturally occurring polymer such as wheat gluten,corn zein, wool, cellulose or starch. The fibre can be derived orobtained from a plant or animal. In particular, the fibre is preferablyextracted from a plant, such as one or more of abaca, bamboo, banana,coir, coconut husk, cotton, flax, henequen, hemp, hop, jute, palm, ramieor sisal. Most preferably the fibre is a sisal fibre

Where the support is obtained or derived from a natural source, thesupport can be biodegradable. It will be appreciated that the provisionof a reinforced biodegradable material will provide benefits,particularly when used in composite materials.

After immersion of the support, it may be removed from the aqueousdispersion of bacterial cellulose and dried. In one embodiment, theprocess of the first aspect of further comprises the steps of

-   -   removing the coated support material from the dispersion; and    -   optionally drying the support material.

The step of removing the coated support material from the dispersion maybe achieved by mechanical extraction of the support, for example, byusing tweezers.

The support material can be dried according to any methods known in theart, for example, air drying, oven drying, freeze drying, drying invacuo, infra-red irradiation etc. The method by which the supportmaterial is dried can impact on the orientation and arrangement of thebacterial cellulose coating on the support material, and can thereforebe modified to manipulate the form of the material produced by the firstaspect of the invention.

In a particular embodiment of the first aspect, the surface coatedsupport material is dried with heating. Preferably, the support materialis dried above room temperature, for example at a temperature of from50° C. to 150° C., preferably 60° C. , 70° C. , 80° C., 90° C., 100° C.,110° C., 120° C., 130° C. or 140° C. The drying temperature can beprovided as a range of temperatures selected from any of the discretetemperatures set out above, for example 70° C. to 90° C. The drying canbe carried our in air or under a vacuum. The drying of the supportmaterial results in a dense nanocellulose layer on the surface of thematerial. The first aspect of the invention therefore provides a processfor the production of a surface coated support material; comprising

-   -   contacting a support material with an aqueous dispersion of        nanocellulose;    -   removing the coated support material from the dispersion; and    -   drying the support material at 70° C. to 90° C., preferably at        80° C. wherein the nanocellulose is provided as a bacterial        cellulose layer on the surface of the support material,        preferably wherein the bacterial cellulose layer is a dense        layer of bacterial cellulose. In a dense layer, the bacterial        cellulose may form a layer which substantially covers the        support material.

Alternatively, the surface coated support material is initiallypartially dried by layering the support material between two pieces ofan absorbent material, such as filter paper. Pressure can be applied tothe upper and/or lower piece of absorbent material, for example by theaddition of a weight to increase the removal of liquid from the supportmaterial. The support material can then be further dried, at atemperature of 30 to 150° C., preferably 40° C., 50° C., 60° C., 70° C.,80° C., 90° C., 100° C., 110C, 120C, 130C or 140C. The dryingtemperature can be provided as a range of temperatures selected from anyof the discrete temperatures set out above, for example, 30° C. to 50°C. The drying is preferably carried out in an air oven. This two stagedrying method results in the formation of hairy “fibres” or a hairysupport, where the nanocellulose is orientated perpendicularly to thesurface of the support material. The first aspect of the inventiontherefore further provides a process for the production of a surfacecoated support material; comprising

-   -   contacting a support material with an aqueous dispersion of        nanocellulose;    -   removing the coated support material from the dispersion; and    -   drying the support material by layering the support material        between two pieces of absorbent material followed by drying in        an air oven at 30° C. to 50° C., preferably at 40° C.;

wherein the nanocellulose of the coating is orientated perpendicularlyto the support surface.

In certain embodiments of a method comprising the steps of

-   -   removing the coated support material from the dispersion; and    -   optionally drying the support material,

the removing step is carried out by filtration of the dispersion, forexample vacuum filtration, or by evaporation, for example under reducedpressure (i.e. under vacuum) and/or heating.

It will be appreciated by the skilled person that the steps of removingthe coated support material from the dispersion and drying the coatedsupport material may be carried out in a single step for example, byevaporation (e.g. by heating and/or under reduced pressure). Forexample, the dispersion comprising the coated support material may beheated to remove the coated support material from the dispersion byevaporation and to dry the support material.

When the coated support material is removed from the dispersion byfiltration, for example, by vacuum filtration, the support material maybe bound together by the nanocellulose (i.e. forming a body comprisingcoated support material bound by the nanocellulose). In embodimentswhere the coated support material is removed from the dispersion byfiltration, the support material may be initially partially dried bylayering the support material between two pieces of an absorbentmaterial, such as filter paper. Pressure can be applied to the upperand/or lower piece of absorbent material, for example by the addition ofa weight to increase the removal of liquid from the support material.The support material may be further dried, at a temperature of 30 to150° C., preferably 40° C., 50° C., 60° C., 70° C., 80° C., 90° C., 100°C., 110° C., 120° C., 130° C. or 140° C. The drying temperature can beprovided as a range of temperatures selected from any of the discretetemperatures set out above, for example, 50° C. to 70° C. The firstaspect of the invention therefore further provides a process for theproduction of a surface coated support material; comprising

-   -   contacting a support material with an aqueous dispersion of        nanocellulose;    -   removing the coated support material from the dispersion by        filtration of the dispersion;    -   drying the support material by layering the support material        between two pieces of absorbent material; and    -   optionally drying in an air oven at 50° C. to 70° C., preferably        at 60° C.

The modified material can be stored at room temperature and pressure.

It has been found that the production of either a dense nanocellulosecoating layer on the surface of the support material or nanocellulosecoated hairy fibres, in which the nanocellulose is orientedperpendicularly to the surface of the support material results in anincrease in surface area of the support material when compared with theunmodified support material.

In a preferred feature of the first aspect of the invention, the supportcan be modified by physical or chemical treatments prior to contact withthe nanocellulose, such as atmospheric or low pressure plasma or coronatreatments, solvent washing or extraction, bleaching, boiling orwashing, for example in a basic solution, such as sodium hydroxidesolution. In particular, the support can be washed with a solvent, suchas an organic solvent (i.e. acetone, ethyl acetate etc. or an alcoholsuch as ethanol, methanol, propanol, butanol etc.) prior to exposing thesupport to an aqueous suspension or slurry of nanocellulose.

The second aspect of the invention relates to a surface coated supportmaterial obtainable by the process of the first aspect of the invention.Preferably the surface coated support material is obtained by theprocess of the first aspect of the invention.

In particular, the second aspect of the invention relates to a supportmaterial surface coated with nanocellulose, wherein the nanocellulose isprovided as a dense nanocellulose coating.

Alternatively, the second aspect of the invention relates to a supportmaterial surface coated with nanocellulose, wherein the nanocellulose ofthe coating is orientated perpendicular to the support surface.

Alternatively, the second aspect of the invention relates to a supportmaterial surface coated with nanocellulose, wherein the support materialis bound together by the nanocellulose.

The third aspect of the invention relates to a composite materialcomprising a reinforcement and a matrix wherein the reinforcementcomprises a surface coated support material obtainable or obtained bythe process of the first aspect of the invention. The composite materialof the third aspect is a cellulose nanocomposite.

In a preferred embodiment of the third aspect of the invention, thematrix comprises cellulose. The cellulose is preferably dispersedthrough the matrix.

The material obtainable by the process of the first aspect can be usedas a reinforcing agent for composite manufacturing. The material cantherefore be combined with any conventional matrix known to a personskilled in the art. Where the material is biodegradable, in order topreserve the renewability and biodegradability of the material,bioderived polymers such as poly(lactic acid) (PLA),polyhydroxyalkanoates (PHA, bacterial polyesters), polycarbonates, ormodified cellulose polymers (cellulose acetate butyrate (CAB) orcellulose butyrate) or cellulose pulp, as well as epoxy resins such asplant based resins (for example acrylated epoxidised soybean oil (AESO)or epoxidised linseed oil) can be used as a matrix.

In a particularly preferred embodiment, the surface coated supportmaterial is used as a reinforcement for a polylactide, for examplepoly-L-lactide (PLLA) to create green hierarchical composites. Theincreased surface area of the surface coated support material increasesthe surface roughness of the surface coated support material and resultsin enhanced mechanical interlocking between the fibres and the matrix.The resulting composite exhibits improved mechanical properties, tensileproperties, visco-elastic properties and flexural properties of thehierarchical composites compared with neat PLLA.

Alternatively, the third aspect of the invention relates to a compositematerial comprising a reinforcement and a matrix wherein the matrixcomprises a surface coated support material obtainable or obtained bythe process of the first aspect of the invention. The matrix comprisingthe material produced by the process of the first aspect of theinvention can be combined with any conventional reinforcement known to aperson skilled in the art. Where the matrix is biodegradable, thereinforcement is preferably also biodegradable.

The fourth aspect of the invention relates to a process for theproduction of a composite material according to the third aspect of theinvention wherein a reinforcement comprising the surface coated supportmaterial obtainable by the first or of the second aspect is impregnated,mixed, or extruded with a matrix, such as a polymer or a resin. Incertain embodiments, the surface coated support material is a surfacecoated support material wherein the support material is bound togetherby nanocellulose. The composite can be manufactured using any suitableprocess such as resin transfer moulding, sheet moulding, resin infusionmoulding, or by powder impregnation, injection moulding and compressionmoulding. For example, the surface coated support material may beimpregnated with a resin, such as acrylated epoxidised soybean oil(AESO) or epoxidised linseed oil and then cured, for example, byheating, optionally in the presence of an initiating species. In anotherexample, the surface coated support material may be dispersed in asolution of a polymer, such as PLA, after which the solvent may beremoved. Alternatively, the surface coated support material may beimpregnated, mixed, or extruded with a polymer powder or a polymerfibre, preferably a thermoplastic polymer, allowing the compositematerial to be heat formed or consolidated into a desired shape.

The fourth aspect of the invention alternatively relates to a processfor the production of a composite material according to the third aspectof the invention wherein a reinforcement is impregnated, mixed, orextruded with a matrix comprising the surface coated support materialobtainable by the first or of the second aspect. The composite can bemanufactured using any suitable process such as resin transfer moulding,sheet moulding, resin infusion moulding, or by powder impregnation,injection moulding and compression moulding.

The fifth aspect of the invention relates to a process for theproduction of a composite material comprising a reinforcement and amatrix wherein the reinforcement comprises a surface coated supportmaterial, wherein the composite material is produced by:

-   -   contacting a support material with an aqueous dispersion of        nanocellulose, wherein the aqueous dispersion of nanocellulose        further comprises a matrix material;    -   removing the composite material from the dispersion by        filtration, preferably vacuum filtration; and    -   optionally drying the composite material.

In certain embodiments, the matrix material is dispersed in the aqueousdispersion of nanocellulose. In other embodiments, the matrix materialis a polymer, preferably a thermoplastic polymer. In another embodiment,the matrix material is a polymer powder or a polymer fibre. The matrixmaterial may be a matrix as described in respect of the third aspect ofthe invention. The composite materials produced by this method maysubsequently be moulded into a desired shape, for example by compressionmoulding or hot pressing. The support material and the drying step maybe as described in respect of the first aspect.

The sixth aspect of the invention relates to an article produced fromthe composite material of the third aspect of the invention or acomposite material produced by the process of the fourth aspect or thefifth aspect. The composite material is particularly provided for use inlow-load applications, including but not limited to packaging, or use inthe automotive, household, sport and/or construction industries. Thearticle of the sixth aspect is preferably produced from a fullybiodegradable composite material.

All preferred features of each of the aspects of the invention apply toall other aspects mutatis mutandis.

Definitions

A dense layer of nanocellulose is a support material coated withnanocellulose wherein the nanocellulose fibres are sufficientlyorientated along the surface of the support material to form asubstantially continuous layer. It will be appreciated that the denselayer can be composed of nanocellulose fibres stacked or layered on topof one another, where those fibres closest to the support will have atleast a portion of the longitudinal axis of the fibre in contact withthe support (i.e. they are support contacting fibres). Furthernanocellulose fibres may be stacked or layered on the support contactingfibres to increase the thickness of the dense layer on the support.These further fibres may not be in contact with the support material.

The support material of the invention is therefore coated withnanocellulose, wherein a portion of the coating is in contact with thesupport surface and wherein the fibres of the portion of the coating incontact with the support surface have at least a part or portion oftheir longitudinal axis in contact with the support surface.

In the dense layer, the support contacting fibres are orientated so thatat least a portion of the longitudinal axis of the fibres is in contactwith the surface of the support. The fibres can lie entirely inalignment (and therefore in contact) with the surface. In this case,substantially all of the longitudinal axis of the fibres is in contactwith the surface of the support. Alternatively, the fibres can be incontact with the support but not lie entirely in alignment. In thiscase, a portion of the longitudinal axis of the fibre is in contact withthe surface. The fibres are in contact with the support and with eachother such that a continuous layer is formed. A dense layer encompassesthe provision of the fibres in an extended form and/or where the fibresare folded.

A hairy fibre or a hairy support is a support material coated withnanocellulose where at least a portion of the nanocellulose isorientated perpendicularly to the surface of the support material. Wherenanocellulose of the coating is “orientated perpendicularly”, in thecontext of this disclosure, it is meant that some, or in someembodiments substantially all, of the nanocellulose, rather than lyingin alignment with the surface of the support material, extends at anangle therefrom (this encompasses not only nanocellulose extending at anangle of 90 degrees relative to the surface of the support material, butalso encompasses nanocellulose which extends at any angle therefrom,rather than lying entirely in alignment with the surface).

The surface morphology of a support material (i.e. whether it is coatedin hairy fibres or a dense layer) can be determined by visuallyinspecting the surface of the support material, for example by scanningelectron microscopy (SEM). As set out in FIG. 1(d), the hairy fibresextend from the surface of the support material. Conversely, as set outin FIGS. 1(b) and (c), the fibres of the dense layer form a coatinglayer on the surface of the support material.

A surface coated support material is a support material, some orpreferably substantially all of the surface of which is coated withnanocellulose. This is intended to encompass a support material coatedwith a dense and a hairy support as described above. This term is alsointended to encompass a support material wherein nanocellulose coats thesupport material and also acts as a binder to bind support materialtogether. Thus, a surface coated support material encompasses a bodycomprising support material bound together by nanocellulose.

The invention may be put into practice in various ways and a number ofspecific embodiments will be described by way of example to illustratethe invention with reference to the accompanying drawings, in which:

FIG. 1 illustrates scanning electron micrographs showing (a) neat sisalfibres, (b), densely bacterial cellulose (BC) coated sisal fibres at lowmagnification, (c) densely BC coated sisal fibres high magnification and(d) “hairy” BC coated sisal fibres;

FIG. 2 illustrates fractured surface of fibre reinforced hierarchicalcomposites at fibre-matrix interface and overall fractured surface. (a)(b) are PLLA-sisal, (c) (d) are PLLA-containing densely nanocellulosecoated sisal fibres, (e) (f) are PLLA-containing hairy cellulose coatedsisal fibres, (g) (h) are PLLA-sisal-BC, (i) (j) are BC-PLLA- containingdensely nanocellulose coated sisal fibres and (k) (1) areBC-PLLA-containing hairy cellulose coated sisal fibres, respectively.(a), (c), (e), (g), (i) and (k) are at lower maginification. (b), (d),(f), (h), (j) and (1) are at higher magnification; and

FIG. 3 illustrates graphs showing the temperature dependency of storagemoduli and tan δ of neat PLLA and its hierarchical composites.

FIG. 4 illustrates a schematic of a method for producing a sisal fibremat and a sisal fibre mat using bacterial cellulose (BC) as a binder.

FIG. 5 illustrates the storage modulus of (a) neat AESO, (b) AESO-sisal,and (c) AESO-sisal-BC as a function of room temperature.

FIG. 6 illustrates the energy dissipation factor (tan δ) of neat AESO,AESO-sisal and AESO-sisal-BC.

The present invention will now be illustrated by reference to one ormore of the following non-limiting examples.

EXAMPLES

Materials

Poly(L-lactic acid) (PLLA) was purchased from Biomer GmbH (L9000, MW≧150kDa, D-content≈1.5%) and was used as the matrix for the production ofhierarchical composites. 1,4-Dioxane (Sigma-Aldrich, ACS Reagent, ≧99%purity) was used as the solvent to dissolve PLLA. Sodium hydroxide(purum grade, pellets) was purchased from Acros Organics. Loose sisalfibres were kindly supplied by Wigglesworth & Co. Ltd. (London, UK).These fibres were grown in East Africa. The harvested crop was left inthe field for approximately 3 to 4 weeks for dew retting in order toallow the combined action of temperature, humidity and bacteria toloosen the fibres. After this retting process, the retted sisal fibreswere placed in a rudimentary tool where the fibres were pulled out byhand, washed with water and sun-dried for a day. Bacterial cellulose(BC) was extracted from commercially available Nata-de-coco (CHAOKOHcoconut gel in syrup, Ampol Food Processing Ltd, Nakorn Pathom,Thailand).

Extraction and Purification of BC

BC was extracted from 10 jars of Nata-de-coco, in batches of 5 jars. Forevery batch, the coconut gels from Nata-de-coco were rinsed three timeswith 5 L of de-ionised water to remove the sugar syrup and blended for 1min using a laboratory blender (Waring Blender LB20EG, ChristisonParticle Technologies, Gateshead, UK). The blended BC was thenhomogenised in 5 L of water at 20,000 rpm for 2 min using a homogeniser(Polytron PT 10-35 GT, Kinematica, Switzerland) and centrifuged at14,000g to remove the excess sugar-water solution. In order to furtherpurify the extracted cellulose, the centrifuged BC was redispersed in 5L of 0.1 M NaOH solution heated to 80° C. for 20 min to remove anyremaining microorganism and soluble polysaccharides. The purified BC wasthen successively centrifuged and homogenised to neutral pH with waterusing the previously described centrifugation-homogenisation step.

Example 1

Coating Sisal Fibres with Nano-Sized BC

A dispersion of 0.1 wt% BC was prepared by homogenising 0.3 g of BC (drybasis) in 300 mL of de-ionsed water. 0.5 g of sisal fibres were immersedand equilibrated in this dispersion for three days at room temperature.After three days of immersion, the fibres were removed from the BC-waterdispersion and dried in two different ways to create (i) a dense(collapsed) BC coating or (ii) “hairy fibres”, with a layer of BCcoating oriented perpendicular away the fibre surface. To create a denselayer BC coating on the fibres, the wet fibres were dried under vacuumat 80° C. overnight. “Hairy fibres” were created by pressing the wetfibres between two filter papers (qualitative filter paper 413, 125 mmin diameter, particle retention of 5-13 μm, VWR, UK) under a weight of 3kg for 10 s to partially dry them. The partially dried “hairy sisalfibres” were then dried in an air oven held at 40° C. The sisal fibrescoated with a dense layer of BC are termed densely coated neat sisalfibres (DCNS) and the “hairy fibres” were termed “hairy neat sisalfibres” (HNSF).

Preparation of Hierarchical Short Fibre Composites

Two different types of hierarchical composites were prepared; (i) BCcoated fibre reinforced PLLA and (ii) BC coated fibre reinforced BC PLLAnanocomposites. For simple hierarchical composites, 2.4 g of (coated)fibres, cut to approximately 10 mm in length, were added into 200 mL of1,4-dioxane. 9.6 g of PLLA pellets were added into this mixture and leftto dissolve overnight at 60° C. under magnetic stirring to create a 20wt % fibre reinforcement in the matrix. The resulting mixture was thenpoured into a Petri dish and dried under vacuum (Edwards Modulyo freezedryer, UK) at room temperature to remove any remaining solvent. Thesolvent was captured by a cold trap, which has the potential to bere-used in the polymer dissolution process. Hierarchical composites withBC dispersed in the PLLA matrix were prepared by immersing 1.8 g of(coated) fibres in 200 mL of 1,4-dioxane and 9.6 g of PLLA pellets wereadded. This mixture was left to dissolve overnight at 60° C. undermagnetic stirring. 0.6 g of freeze-dried BC was added into 150 mL of 1,4dioxane in a separate beaker and homogenised at 20,000 rpm for 2 min.This BC dispersion was then added into the PLLA polymer solutioncontaining sisal fibres and stirred gently to ensure homogeneousdispersion of BC in the fibre-polymer solution. This mixture was thenvacuum dried at room temperature to remove any remaining solvent.

Production of Hierarchical Composites

The previously produced sisal fibres-PLLA-BC “prepregs” were injectionmoulded into flexural bars with a sample dimension of 80 mm×12 mm×3.5 mmusing a piston injection moulder (Hakke Minijet, Thermo Scientific,Hampshire, UK). Tensile test specimens (BS ISO 527:1996 type V) was alsoinjection moulded using the same piston injection moulder. The tensiledog bone test specimens have an overall length of 60 mm, gauge length of10 mm, thickness of 3 mm and the narrowest part of the sample was 3 mm.The barrel temperature and the mould temperature were held at 190° C.and 70° C., respectively. Neat PLLA was injection moulded with aninjection pressure and time of 400 bar and 30 s and a post-pressure andtime of 200 bar and 30 s. (BC Coated) sisal fibres reinforced PLLA wasinjected with an injection pressure and time of 500 bar and 30 s and apost-pressure and time of 200 bar and 30 s. Due to the increase inviscosity of the polymer melt when BC was dispersed both on the surfaceof sisal fibres and in the PLLA matrix, the hierarchical composites with(BC coated) sisal fibre and BC dispersed in the matrix was injected withan injection pressure and time of 600 bar and 30 s and a post-pressureand time of 200 bar and 30 s.

Characterisation of BC Coated Sisal Fibres and its PLLA HierarchicalComposites

Scanning Electron Microscopy (SEM)

SEM was conducted to characterise the surface morphology of neat and BCcoated sisal fibres. It was also used to characterise the fracturedsurface of the hierarchical composites. SEM was performed using ahigh-resolution field emission gun scanning electron microscope (LEOGemini 1525 FEG-SEM, Oberkochen, Germany). The accelerating voltage usedwas 5 kV. Prior to SEM, all the samples were fixed onto SEM stubs usingcarbon tabs and coated with Cr for 1 min and 75 mA.

Specific Surface Area (BET) Measurements

Nitrogen adsorption/desorption isotherms were conducted to determine thespecific surface area of neat and BC coated sisal fibres. Thismeasurement was performed using a surface area and porosity analyser(TriStar 3000, Micrometerics Ltd, Dunstable, UK). The specific surfacearea was calculated using the Brunauer-Emmett-Teller (BET) equation.Prior to the measurement, the fibres were degassed at 80° C. overnightto remove any adsorbed water molecules.

Single Fibre Tensile Properties of Neat and BC Coated Sisal Fibres

Single fibre tensile tests were performed to investigate the effect ofBC coating on the tensile properties of sisal fibres. The test wasconducted at room temperature in accordance to ASTM D-3822-07, using aTST 350 tensile testing rig (Linkam Scientific Instrument Ltd, Surrey,UK) at room temperature equipped with 200 N load cell. The gauge lengthand crosshead speed used were 20 mm and 1 mm min⁻¹, respectively. Asingle sisal fibre was fixed at either end of a testing card usingsuperglue. A total of 10 measurements were conducted for each type offibre to obtain a statistical average. The fibre diameter was evaluatedusing an optical microscope (Olympus BX 41 M reflective microscope,Essex, UK) and the tensile properties of the fibres were calculated byassuming the fibres possessed a cylindrical geometry.

Mechanical Properties of the Hierarchical Composites

Tensile and flexural (3-point bending) properties of sisal fibrereinforced PLLA hierarchical composites were conducted in accordance toBS EN ISO 527: 1996 and BS EN ISO 178: 2003, respectively. The testswere performed using an Instron universal testing machine (Instron 4466,Instron Corporation, Massachusetts, USA) with a load cell of 10 kN atroom temperature and 50% relative humidity. The testing speed used fortensile and flexural tests were 1 mm min⁻¹ and 20 mm min⁻¹,respectively. A span of 55 mm (span to thickness ratio=16) was used forflexural test.

Differential Scanning Calorimetry (DSC) of Hierarchical Composites

The crystallisation and melt behaviour of (BC coated) fibre reinforcedPLLA hierarchical (nano)composites were investigated using DSC (DSCQ2000, TA Instruments, West Sussex, UK) in a He atmosphere.Approximately 20 mg of sample was used in the measurement. Aheat-cool-heat regime was employed during the test. The sample was firstheated from room temperature to 210° C. at a heating rate of 10° C.min⁻¹ before cooling it to room temperature at a cooling rate of 50° C.min ⁻¹. The sample was then re-heated to 210° C. at a heating rate of10° C. min⁻¹. The crystallinity (based on 1^(st) heating curve) of thecomposites produced was calculated using the equation:

$\begin{matrix}{\chi_{C} = {\frac{{\Delta \; H_{m}} - {\Delta \; H_{c}}}{\left( {1 - f} \right)\Delta \; H_{m}^{o}} \times 100\%}} & \lbrack 1\rbrack\end{matrix}$

where χ_(c), is the crystallinity of the composite, ΔH_(m), ΔH_(c), fand ΔH_(m) ⁰ are the melting enthalpy and cold crystallisation enthalpydetermined from DSC curves, weight fraction of the reinforcing phase (20wt %) and the melting enthalpy of pure crystalline PLLA (93.76 J g⁻¹(Mathew A P, Oksman K, Sain M. J Appl Polym Sci. 2006;101(1):300-310.)),respectively.

Dynamic Mechanical Analysis (DMA) of the Hierarchical Composites

The visco-elastic behaviour of the composites was investigated using DMA(Tritec 2000, Triton Technology Ltd, Keyworth, UK). DMA was performed insingle beam cantilever bending mode with a gauge length of 10 mm. Thesample has a thickness and width of approximately 3 mm. The storagemodulus, loss modulus and energy dissipation factor (tan δ) weremeasured from 30° C. to 100° C. at a heating rate of 2° C. min⁻¹ and afrequency of 1 Hz.

Results and Discussion

Morphology of BC Coated Sisal Fibres

FIG. 1 shows the SEM images of neat sisal fibres, densely BC coatedsisal fibres and “hairy BC coated sisal fibres”. The morphology ofdensely coated sisal fibres with BC (FIG. 1b and FIG. 1c ) resembles theBC coated fibres obtained by culturing the fibres with Acetobacter in abioreactor (Pommet M, Juntaro J, Heng J Y Y, Mantalaris A, Lee A F,Wilson K, et al. Biomacromolecules. 2008;9(6):1643-1651). In addition tothis, it was also possible to obtain true “hairy BC coated sisal fibres”(FIG. 1d ). The loading fraction of BC on sisal fibres was found to be10 wt % (by measuring the mass of dry sisal fibres before and afterimmersion in BC dispersion in both DCNS and HNSF). The fast drying rateof the coated fibres under vacuum resulted in the collapsing of BCnanofibrils onto the surface of sisal fibres (FIG. 1b and FIG. 1c ). Bypressing the wet BC coated sisal fibres between filter papers, thefibres were partially dried by filter papers. During this process, thewet BC nanofibrils were drawn into the filter paper by the capillaryforces. Combining this with the slow drying rate of the coated fibres(which prevents the collapse of the nanofibrils), the BC coating is nownot arranged in a dense layer but the BC nanofibrils were orientedperpendicularly (“hairy fibres”) to the surface of sisal fibres.

BET Surface Area of BC Coated Sisal Fibres

TABLE 1 Table 1: BET surface area, single fibre tensile modulus andtensile strength of neat and BC coated sisal fibres; dense layer and“hairy fibres”, respectively BET surface Single fibre tensile propertiesarea Tensile modulus Tensile Strength Sample (m² g⁻¹) (GPa) (MPa) Neatsisal fibres 0.097 ± 0.008 23.2 ± 3.3 529 ± 91 DCNS fibres 0.770 ± 0.03014.1 ± 1.5 297 ± 30 HNSF fibres 0.485 ± 0.029 23.3 ± 2.8 474 ± 53

Table 1 tabulates the measured BET surface area of neat and BC coatedsisal fibres. The surface area of BC coated fibres can be increased byas much as 8 times when compared to neat sisal fibre. Hairy fibres havea lower surface area than DCNS even though both types of fibres havesimilar BC loading.

Tensile Properties of Neat and BC Coated Sisal Fibres

Chemically treated natural fibres generally have reduced single fibretensile properties (Kalia S, Kaith B S, Kaur I. Pretreatments of NaturalFibers and their Application as Reinforcing Material in PolymerComposites-A Review. Polym Eng Sci. 2009;49(7):1253-1272). Pickering KL, Li Y, Farrell R L, Lay M. Interfacial modification of hemp fiberreinforced composites using fungal and alkali treatment. J BiobasedMater Bioenergy. 2007;1(1):109-117 studied the effect of enzymetreatment on the properties of single hemp fibres. The authors showedthat the single fibre tensile strength of enzyme treated hemp fibresdecreased by as much as 50% compared to untreated fibres. The singlefibre tensile properties of neat and BC coated sisal fibres are shown inTable 1. The tensile properties of neat sisal fibres in this study is inagreement with values obtained by various researchers in the literature(Bismarck A, Mishra S, Lampke T. Plant fibers as reinforcement for greencomposites. In: Mohanty A K, Misra M, Drzal L, editors. Natural fibers,biopolymers and biocomposites, Boca Raton: CRC Press; 2005).

When sisal fibres are coated with a dense layer of BC (DCNS), its fibretensile modulus and tensile strength decreased by 40% and 45%,respectively. The fibre's tensile modulus remained unchanged and thefibre's tensile strength reduced only by 10% (but still within the errorof neat sisal fibres) when the fibres are wet pressed between filterpapers to create “hairy sisal fibres”.

Mechanical Properties of Composites

In order to investigate the effect of BC coating on the mechanicalproperties of sisal fibre reinforced PLLA hierarchical composites,tensile and flexural tests were conducted. These results are shown inTable 2

TABLE 2 Table 2: Summary of mechanical properties of neat PLLA and itscomponents E_(T), σ_(T), E_(F), σ_(F) indicate tensile modulus, tensilestrength, flexural modulus and flexural strength, respectively. SampleE_(T) (GPa) σ_(T) (MPa) E_(F) (GPa) σ_(F) (MPa) Neat PLLA 0.97 ± 0.0262.6 ± 1.0 3.70 ± 0.04 86.1 ± 6.9 PLLA-sisal 1.28 ± 0.03 58.7 ± 1.0 4.85± 0.10 105.6 ± 1.5  PLLA-DCNS 1.35 ± 0.03 57.3 ± 1.3 5.19 ± 0.07 99.2 ±2.8 PLLA-HNSF 1.29 ± 0.03 57.8 ± 1.6 4.96 ± 0.16 102.0 ± 2.5 PLLA-sisal-BC 1.46 ± 0.02 60.9 ± 1.9 5.74 ± 0.05 100.0 ± 2.2 PLLA-DCNS-BC 1.63 ± 0.04 67.8 ± 1.2 6.19 ± 0.08 95.5 ± 2.3 PLLA-HNSF-BC1.59 ± 0.05 69.2 ± 1.2 5.77 ± 0.13 96.8 ± 2.0

It can be seen that with (BC coated) sisal fibre as reinforcement, thetensile moduli for all samples increased. The increase in tensilemodulus of the hierarchical composites was more apparent when BC is bothdispersed in the matrix and coated on sisal fibres (PLLA-sisal-BC,PLLA-DCNS-BC and PLLA-HNSF-BC). With BC dispersed in the matrix and onthe fibres, both the matrix and the fibre-matrix interface could bereinforced (or stiffened). This led to the observed improvements intensile modulus of PLLA-DCNS-BC by as much as 72% when compared to neatPLLA and 30% when compared to PLLA-sisal hierarchical composites.

The tensile strength of the hierarchical composites, on the other hand,showed slightly different trend compared to tensile modulus. A decreasein tensile strength was observed when PLLA is reinforced with (BCcoated) sisal fibres, with no BC dispersed in the matrix. When thehierarchical composites are reinforced with BC in the PLLA matrix(PLLA-HNSF-BC), the tensile strength improved by as much as 11% whencompared to neat PLLA and 21% when compared to PLLA-DCNS. With BCdispersed in the matrix, the matrix is stiffened.

Table 2 shows the flexural properties of the composites. It can be seenthat the flexural modulus increased with fibre/BC reinforcement. Theflexural modulus of the hierarchical composites with BC dispersed in thematrix (PLLA-DCNS-BC) improved by as much as 67% when compared to neatPLLA and 40% when compared to hierarchical composites without BCdispersed in the matrix. As aforementioned, this is due to matrixstiffening effect induced by nano-sized reinforcement in PLLA matrix.The flexural strength of the all the composites increased when comparedto neat PLLA. An increase in flexural strength by as much as 23% wasobserved. It seems, however, that the BC coating on sisal fibres and/orin the matrix has no effect on the overall flexural strength of thecomposites. Due to the low fibre volume fraction of short fibrecomposites, individual fibre failure is isolated and therefore,microbuckle bands and kinkbands do not form (Greenhalgh ES. Failureanalysis and fractography of polymer composites. Cambridge: WoodheadPublishing Ltd and CRC Press LLC; 2009.). Instead, a shear failure ofshort-fibre composites is usually observed. Flexural failure ofshort-fibre composites is accompanied by tension on the bottom surfaceand compression on the top surface of the specimens (Jeng C C, Chen M.Flexural failure mechanisms in injection-moulded carbon fibre/PEEKcomposites. Compos Sci Technol. 2000;60(9):1863-1872.), which results inshear fracture in the mid-section of the specimen.

Fractography of Hierarchical Composites

The fractured surface of the composites failed in tension is shown inFIG. 2. When PLLA is reinforced by sisal fibres, fibre debonding (FIG.2a ) and fibre pull out can be clearly seen (FIG. 2b ). This is a directresult in poor interfacial adhesion between the fibre and the matrix,which results in the poor stress transfer. This resulted in poor tensilestrength of PLLA-sisal when compared to neat PLLA. When sisal fibres arecoated with BC, the fibre-matrix is improved as no fibre debonding canbe observed (FIG. 2c-f ). Single fibre pull out study in previous study(Pommet M, Juntaro J, Heng J Y Y, Mantalaris A, Lee A F, Wilson K, etal. Surface modification of natural fibers using bacteria: Depositingbacterial cellulose onto natural fibers to create hierarchical fiberreinforced nanocomposites. Biomacromolecules. 2008;9(6):1643-1651) hasalso shown the interfacial adhesion between the BC coated fibre and PLLAmatrix is enhanced. Even though no fibre debonding was observed, thetensile strength of PLLA-DCNS and PLLA-PCNS decreased when compared toneat PLLA. Failures in short-fibre composites can be classified into twotypes; T-fibre fracture (crack plane oriented transverse to fibreorientation—high fracture energy) and L-fibre fracture (crack planeoriented parallel to fibre orientation—low fracture energy) (GreenhalghE S. Failure analysis and fractography of polymer composites. Cambridge:Woodhead Publishing Ltd and CRC Press LLC; 2009). In general,short-fibre composites exhibit a combination of fractured failures. Theoverall fractured surface of PLLA-DCNS and PLLA-HNSF showed L-fibrefractured surface as the dominant mechanism. This explained the poortensile strengths of these composites even though the fibre-matrixinterface is enhanced through mechanical interlock.

However, when BC is dispersed in the fibre reinforced PLLA composites,the overall fractured surface and hence, fractured mechanism, wasmodified. No significant fibre debonding or fibre pull out can beobserved in PLLA-sisal-BC, PLLA-DCNS-BC and PLLA-HNSF-BC composites inFIG. 2g -1. This is accompanied by the improved mechanical properties(both tensile strength and modulus) of the hierarchical composites whencompared to neat PLLA.

Crystallisation and Melt Behaviour of the Hierarchical Composites

The thermal behaviour of the composites were characterised by DSC andtheir characteristic temperatures such as glass transition temperatures(T_(g)), crystallisation temperatures (T_(c)) and melt temperature(T_(m)) on the first and second heating are tabulated in Table 3.

TABLE 3 Table 3: Crystallisation and melt behavior of neat PLLA and itsfibre/BC reinforced hierarchical composites. T_(g), T_(c), T_(m) andχ_(c) are glass transition temperature, crystallisation temperature,melt temperature and crystallinity of the composites, respectively.Sample Heating T_(g) (° C.) T_(c) (° C.) T_(m) (° C.) χ_(c) (%) PLLA1^(st) 63 113 171 14 2^(nd) 61 110 169 PLLA-sisal 1^(st) 57 100 168 172^(nd) 59 103 168 PLLA-DCNS 1^(st) 57 88 168 13 2^(nd) 62 93 169PLLA-HNSF 1^(st) 57 94 166 12 2^(nd) 57 94 166 PLLA-sisal-BC 1^(st) 5583 165 18 2^(nd) — — 168 PLLA-DCNS-BC 1^(st) 56 85 163 14 2^(nd) — — 166PLLA-HNSF-BC 1^(st) 54 81 165 19 2^(nd) — — 167

The T_(g) of PLLA in the composites was slightly lower when compared toneat PLLA. There are also no significant changes in the melt temperatureof the composites but the crystallisation behaviour of the compositeschanged significantly compared to neat PLLA. A lowering of T_(c) can beobserved in composites reinforced with sisal fibres. Cellulosic fibresare known to act as a nucleation sites for PLLA crystallisation(Suryanegara L, Nakagaito A N, Yano H. The effect of crystallization ofPLA on the thermal and mechanical properties of microfibrillatedcellulose-reinforced PLA composites. Compos Sci Technol.2009;69(7-8):1187-1192). With BC coating on sisal fibres, T, was loweredeven further from 100° C. to 90° C. BET measurements showed an increasein the surface area of coated fibres. This led to more nucleation sitesfor PLLA crystals to nucleate and therefore, the further lowering ofT_(c). It should also be noted that there are no T_(g) or T_(c) observedin the second heating of the hierarchical composites with a BCreinforced matrix. The crystallinity of the composites did not seem tobe affected with the addition of sisal fibres and/or BC. An exotherm wasobserved around 150° C. (results not shown). This is consistent with thesolid-solid crystal transformation of the α′ form to the a form of PLLA(Kawai T, Rahman N, Matsuba G, Nishida K, Kanaya T, Nakano M, et al.Crystallization and melting behavior of poly (L-lactic acid).Macromolecules. 2007;40(26):9463-9469).

Visco-Elastic Behaviour of Hierarchical Composites

The visco-elastic properties of neat PLLA and its hierarchicalcomposites as a function of temperature are shown in FIG. 3. The storagemoduli of the hierarchical composites are higher than that of neat PLLA.By reinforcing PLLA with BC and/or sisal fibres, a stiffer material canbe produced. This result corroborates with the tensile and flexuralmoduli, which suggests that the (BC coated) sisal fibres have a stronginfluence on the visco-elastic properties of the resulting(nano)composites. The storage moduli stayed relatively constant untilT_(g), when a sharp decrease can be seen. This corresponds to thesoftening of the polymer. It can also be seen that by coating thesurface of sisal fibres with BC or dispersing BC in the polymer matrix,the storage modulus can be improved when compared to neat PLLA (by atleast 52%) or neat sisal reinforced PLLA composites (by at least 15%).Different visco-elastic behaviour between composites with and without BCdispersed in the matrix (FIG. 3a-b ) can also be observed beyond themechanical T_(g) of the hierarchical composites. Crystallisation of thematrix occurred at lower temperatures when BC was dispersed in thematrix.

The tan δ of neat PLLA and its hierarchical composites are shown in FIG.3c-d . Tan δ, which measures the damping properties of the material, isalso determined by the quality of fibre-matrix adhesionBaltazar-y-Jimenez A, Juntaro J, Bismarck A. J Biobased Mater Bioenergy.2008;2(3):264-272). A large tan δ amplitude indicates a weak interfacewhere a small tan δ amplitude indicates stronger interface (van denOever M J A, Bos H L, van Kemenade M. Appl Compos Mater.2000;7(5-6):387-402). The amplitude of tan δ is lower for BC coatedsisal fibre reinforced PLLA and composites with BC dispersed in thematrix. Table 4 tabulates the mechanical T_(g) (taken as the peak of tanδ) and improvements in storage moduli as a result of BC and fibrereinforcement.

TABLE 4 Table 4: Mechanical T_(g), storage moduli (G′) and improvementsin storage moduli of the hierarchical composites. Mechanical G′ @ 30° C.Improvements in G′ Sample T_(g) (° C.) (GPa) over neat PLLA (%) PLLA 731.57 — PLLA-sisal 69 2.07 32 PLLA-DCNS 68 2.52 61 PLLA-HNSF 66 2.52 61PLLA-sisal-BC 63 2.49 59 PLLA-DCNS-BC 69 2.39 52 PLLA-HNSF-BC 61 2.64 69

The mechanical T_(g) of PLLA was determined to be 73° C. and decreasedwith BC/fibre reinforcement. This result also corroborates with DSC, asit shows lowering of T_(g). DMA results showed an improved fibre-matrixinterface as a result of BC coating/dispersion.

The present application therefore discloses the production of randomlyoriented short sisal fibre reinforced PLLA hierarchical composites withimproved properties over neat PLLA. The application discloses a novelmethod of producing a surface coated support material based on slurrydipping to coat in particular sisal fibres with nano-sized bacterialcellulose. This process provides a cost effective and alternative methodto modify the surface of fibres. This process can be used to produceeither a dense nanocellulose coating layer on the surface of sisalfibres or nanocellulose coated hairy fibres, in which the nanocelluloseis oriented perpendicularly to the surface of the fibres. BET surfacearea measurements showed an increase in surface area of the fibres by asmuch as 800% when compared to neat sisal fibres. The flexural modulus ofthe composites using the surface coated support material improved by asmuch as 67% and their flexural strength increased by 23% when comparedto neat PLLA. DMA also suggests an enhanced fibre-matrix interface (areduction in the height of tan δ) and higher storage moduli whencompared to neat PLLA. This new type of short fibre composites offers apromising alternative (on the basis of cost versus performance) to theindustry as no chemical modifications or plasma treatments are requiredto produce biodegradable composites with improved properties.

Example 2

Production of Sisal Fibre Mat with and without Utilising BC as theBinder

16 g of sisal fibres, cut into 10 mm in length, were immersed into 2 Lof de-ionised water and left for 24 hours for complete swelling offibres. In order to produce fibre preforms made of sisal fibres, thisdispersion of fibres was filtered under vacuum using filter paper(qualitative filter paper 413, particle retention of 5-13 μm, 125 mm indiameter, VWR, UK). The filter cake was then removed and pressed under aweight of 1 t for 2 min. This process was repeated prior to drying ofthe fibres in at oven held at 60° C. overnight. Fibre preforms utilisingBC as binder to bind the sisal fibres together was also produced.Firstly, 1.7 g of BC (on a dry weight basis) was homogenised at 20,000rpm in 2 L of water for 2 min. 16 g of sisal fibres, cut into 10 mm inlength were immersed into this BC-water dispersion and left for 24 hoursfor complete swelling of the fibres. The sisal fibre volume fraction is90 wt.-%. This BC-sisal fibre-water dispersion was then filtered undervacuum, pressed twice under a weight of 1 t for 2 min and dried in anoven overnight held at 60° C. A schematic of this fibre mat-makingprocess is shown in FIG. 4.

Production of randomly oriented sisal fibre mat reinforced acrylatedepoxidised soybean oil (AESO) composites

The fibre reinforced (nano)composites were manufactured using vacuumassisted resin infusion. AESO resin was mixed with 5 wt.-% of initiator(Luperox P, purity>98%, Aldrich, UK) relative to the mass AESO. Thedegassing of the resin was performed at 80° C. under vacuum. At thistemperature, the polymerisation reaction will not proceed, as thethermal initiation temperature of the initiator is 104° C. Prior toresin infusion, the fibre mats (with and without BC as the binder) wasfurther dried at 120° C. under a weight of 250 kg for 15 min. The fibrepreforms were vacuum bagged on a one-sided mould, i.e. the tooling sideand AESO was drawn into the vacuum bag under the driving force createdby vacuum. The resin and the vacuum bagging were held at 80° C. duringthe infusion process to reduce the viscosity of

AESO. The resin was then cured at 110° C. for 2 h and post cured at 130°C. for another 2 h prior to cooling down to room temperature overnight.During the curing process, the vacuum bagging was left under vacuum toimprove consolidation of the composites. The resulting fibre reinforcedcomposites possess a total fibre volume fraction of 40 vol.-%. Neat AESOwas polymerised in a rectangle mould under identical conditions.Composites reinforced with sisal fibres and sisal fibres with BC as thebinder are termed AESO-Sisal and AESO-Sisal-BC, respectively.

Characterisation

Mechanical Properties of the Sisal Fibre Reinforced (Nano) Composites

Tensile and flexural (3-point bending) properties of the sisal fibrereinforced AES 0 (nano)composites were conducted in accordance to ASTMD3039 and ASTM D790, respectively.

The tests were performed using an Instron universal testing machine(Instron 4505, Instron Corporation, Massachusetts, USA) with load cellsof 10 kN (for tensile test) and 1 kN (for flexural test), respectively,at room temperature. Prior to the tests, the (nano)composites were cutinto dimensions of 120 mm×15 mm×3 mm for tensile tests and 80 mm×15 mm×3mm for flexural tests, respectively. Glass fibre reinforced compositeswas used as the end tabs for the tensile test specimens. The gaugelength used for tensile tests and the span for flexural test were both60 mm. The testing speed used was 1 mm min⁻¹ for all tests. Straingauges (FLA-2-11, Techni Measure, Warwickshire, UK) were used in tensiletests to provide accurate description of the sample strain. A total of 5samples were tested for each specimen.

Dynamic Mechanical Analysis (DMA) of the Sisal Fibre Reinforced (Nano)Composites

The visco-elastic behaviour of the (nano)composites was investigatedusing DMA

(Tritec 2000, Triton Technology Ltd, Keyworth, UK). DMA was performed insingle beam cantilever bending mode with a gauge length of 10 mm. Thesample has a thickness and width of approximately 3 mm. The storagemodulus, loss modulus and energy dissipation factor (tan 6) weremeasured from −100° C. to 180° C. at a heating rate of 5° C. min⁻¹ and afrequency of 1 Hz.

Results and Discussion

Mechanical Properties of Sisal Fibre Reinforced (Nano) Composites

In order to investigate the effect of utilising BC as the binder forsisal fibres on the mechanical properties of sisal fibre reinforced AESOcomposites, tensile and flexural tests were conducted and the resultsare shown in Table 5.

TABLE 5 Mechanical properties of neat AESO and its fibre reinforced(nano)composites. E_(T), σ_(T), E_(F) and σ_(T) indicate tensilemodulus, tensile strength, flexural modulus and flexural strength,respectively. Sample E_(T) (GPa) σ_(T) (MPa) E_(F) (GPa) σ_(F) (MPa)Neat AESO 0.40 ± 0.01  4.1 ± 0.1 0.57 ± 0.03 28.9 ± 0.2 AESO - Sisal3.17 ± 0.19 18.4 ± 0.9 6.07 ± 0.49 95.3 ± 4.1 AESO - Sisal - 5.63 ± 0.3931.4 ± 0.5 13.03 ± 0.91  177.7 ± 10.5 BC

It can be seen from this table that the use of BC as the binder haspositive impact on both the tensile and flexural properties of thecomposites. The tensile modulus of AESO-sisal improved by 7 timescompared to neat AESO. When BC was used as the binder (AESO-sisal-BC),the tensile modulus improved by 13 times compared to neat AESO and 77%compared to AESO-sisal. The tensile strength of the (nano)compositesshowed similar trend as well, whereby AESO-sisal-BC showed animprovement of 400% and 73%, respectively compared to neat AESO andAESO-sisal. Improvements in the mechanical properties of the compositesare not limited to the tensile properties only. The flexural propertiesof the sisal fibre reinforced (nano)composites also showed significantimprovement over neat AESO (see table 5). When BC is used as the binder,the flexural modulus and strength of the (nano)composites improved by 22times and 114%, respectively compared to neat AESO, and 200% and 86%,respectively when compared to AESO-sisal. The observed improvement canbe attributed (i) enhanced stress transfer among the fibre mats when BCwas used as the binder and (ii) the use of BC as the nano-reinforcementfor AESO that stiffens the matrix, which was estimated to posses aYoung's modulus of 114 GPa.

Visco-Elastic Behaviour of Sisal Fibre-Reinforced (Nano) Composites Thevisco-elastic properties of neat AESO and its sisal fibre reinforcednanocomposites are shown in FIG. 5. From this figure, it can be seenthat the storage moduli of the (nano)composites is higher than that ofneat AESO. When using BC as the binder for sisal fibres, a stiffermaterial can be produced (AESO-sisal-BC). This result corroborates withthe mechanical properties of AESO-sisal and AESO-sisal-BC shown in Table5. The storage moduli of the materials stayed relatively constant untila sharp decrease can be seen around 40° C.-50° C., where thiscorresponds to the softening of the matrix. The storage moduli and theimprovements in storage moduli of the (nano)composites are tabulated inTable 6. An improvement over neat AESO of 95% and 246% were observed forAESO-sisal and AESO-sisal-BC.

TABLE 6 Mechanical T_(g), storage moduli (G′) and improvements instorage moduli of the sisal fibre reinforced (nano)composites.Mechanical G′ @ −100° C. Improvements in G′ Sample T_(g) (° C.) (GPa)over neat AESO (%) Neat AESO 50 0.53 — AESO - Sisal 53 1.03 95 AESO -Sisal - BC 53 1.82 246

The tan δ of neat AESO and its (nano)composites is shown in FIG. 6 andthe mechanical T_(g) (the peak of tan δ ) is tabulated in Table 6. Tanδ, which measures the damping properties of a material is alsodetermined by the quality of the fibre-matrix interface. Large tan δamplitude indicates weak interface whereas a small tan δ amplitudeindicates strong fibre-matrix interface. It can be seen from FIG. 6 thatAESO-sisal-BC showed lower tan δ amplitude compared to AESO-sisal.Therefore, the significant improvement seen in AESO-sisal-BC over bothneat AESO and AESO-sisal can be attributed to the enhancedfibre-fibre/fibre-matrix stress transfer. The rigid skeletal of BC andthe formation of BC network within the matrix also contributes to thissignificant improvement in the properties of AESO-sisal-BC.

1-22. (canceled)
 23. A material that is coated with nanocellulose, wherein at least a portion of the nanocellulose is orientated perpendicular to a surface of the material, wherein the material is derived from a plant.
 24. The material of claim 23, wherein the nanocellulose binds together the material.
 25. The material of claim 23, wherein the nanocellulose is bacterial cellulose.
 26. The material of claim 23, wherein the nanocellulose is nanofibrillated cellulose.
 27. The material of claim 23, wherein the nanocellulose has an average width of from 0.5 to 100 nm.
 28. The material of claim 23, wherein the nanocellulose has an average width of from 1 to 50 nm.
 29. The material of claim 23, wherein the nanocellulose has an average width of from 5 to 20 nm.
 30. The material of claim 23, wherein the nanocellulose has an average length of from 0.5 to 1000 micrometers.
 31. The material of claim 23, wherein the nanocellulose has an average length of from 1 to 500 micrometers.
 32. The material of claim 23, wherein the nanocellulose has an average length of from 5 to 300 micrometers.
 33. The material of claim 23, wherein the nanocellulose has an average length of from 10 to 150 micrometers.
 34. The material of claim 23, wherein the material is in a form of fiber.
 35. The material of claim 23, wherein the material is a support material.
 36. The material of claim 35, wherein the support material is hydrophilic.
 37. The material of claim 23, wherein the material further comprises a synthetic polymer.
 38. The material of claim 37, wherein the synthetic polymer is poly(lactic acid) (PLA), polyhydroxyalkanoate (PHA), cellulose acetate butyrate (CAB), cellulose butyrate, polypropylene (PP), polystyrene (PS), polymethylmetharylate (PMMA), lyocell, rayon, acrylated epoxidised soybean oil (AESO), or epoxidised linseed oil.
 39. The material of claim 23, wherein the material is derived from one or more of flax, abaca, bamboo, banana, coir, coconut husk, cotton, henequen, hemp, hop, jute, palm, ramie, or sisal.
 40. The material of claim 39, wherein the material is derived from flax. 